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Methane (CH4)
Ed DlugokenckyESRL
Global Monitoring DivisionCarbon Cycle Group
Why is CH4 important?• 2nd-largest anthropogenic GHG RF• Important in atmospheric chemistry
– Affects cleansing capacity (OH) – GHG lifetimes– Source of stratospheric H2O – indirect RF– Source of tropospheric O3 – indirect RF
• Potential large climate feedbacks in Arctic• Good target to reduce RF short-term
– Quick response (lifetime ≈ 10 years)– Cost effective
• Uncertainties on budget still large
Goals of Research
• Measure spatial/temporal distribution of CH4abundance (and its isotopic composition)– Input for RF calculation
• Determine emission rates– Verify national emissions estimates
• Assess compliance with treaty obligations
• Understand processes– Develop predictive capability
• How will emissions respond to changing climate?
Air sampling platforms
Samples returned to Boulder
RF ~ 0.5 W m-2
Mass ~ 5 Gt
Emissions = 0.55 Gt yr-1
Emissions by Source:Inverse Modeling
Air Parcel Air Parcel
Air Parcelwind wind
Sample Sample
OH + CH4Emissions
80
200
5080
An. emissions (Tg/yr)20
70
40
Future Work• Reduce uncertainties in emissions estimates
– Enhance sampling network– Improvements to models
• Identify changes in Arctic CH4 emissions– Measurements planned for Cherskii and Tiksi– Discussions with USGS for Yukon Basin
• Verify North American emissions– CH4 measurements from tall towers
Total Global Emissions
Q = d[CH4]/dt + [CH4]/τWhere Q = emissions
τ = CH4 lifetime = 8.9 years
Q = 556 ± 10 Tg CH4 yr-1
Average Emissions = 556 ± 10 Tg CH4 yr-1
For 1990-2006: Trend in Emissions = -0.7 ± 0.6 Tg CH4 yr-2
Generally consistent with approach to steady state.
Distribution of Emissions
• Observe N to S Difference ≈ 82 ppb• Es = – f(N-S) + [CH4]s/τ
where f = 1 yr-1
• Es ≈ 160 Tg CH4 yr-1 or
S. hemisphere emissions ≈ 30%
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